1. Field of the Invention
Exemplary aspects of the present disclosure generally relate to a fixing device and an image forming apparatus, and more particularly, to a fixing device for fixing a toner image on a recording medium and an image forming apparatus including the fixing device.
2. Description of the Related Art
Related-art image forming apparatuses, such as copiers, facsimile machines, printers, or multifunction printers having at least one of copying, printing, scanning, and facsimile capabilities, typically form an image on a recording medium according to image data. Thus, for example, a charger uniformly charges a surface of an image bearing member (which may, for example, be a photoconductive drum); an optical writer projects a light beam onto the charged surface of the image bearing member to form an electrostatic latent image on the image bearing member according to the image data; a developing device supplies toner to the electrostatic latent image formed on the image bearing member to render the electrostatic latent image visible as a toner image; the toner image is directly transferred from the image bearing member onto a recording medium or is indirectly transferred from the image bearing member onto a recording medium via an intermediate transfer member; a cleaning device then cleans the surface of the image carrier after the toner image is transferred from the image carrier onto the recording medium; finally, a fixing device applies heat and pressure to the recording medium bearing the unfixed toner image to fix the unfixed toner image on the recording medium, thus forming the image on the recording medium.
In known image forming apparatuses, the unfixed toner image is heated while the record medium carrying the unfixed toner image is interposed between a fixing member and a pressing member, thereby melting and softening a developing agent in the unfixed toner image to fix the toner to the fixing member.
When heating the fixing member to a predetermined temperature by a heat source, if the desired temperature of the fixing member is achieved in a short period of time, even omitting a pre-heating process in a standby state does not have a large affect on the usability of a user, thereby allowing significant reduction in consumption energy. In view of the above, the fixing member employs parts having a low heat capacity such as a thin roller and a thin belt formed of a metal base member on which an elastic rubber layer is disposed. Further, in order to heat the fixing member quickly, an IH (induction heating) type heater with high heating efficiency is used, on top of a halogen heater, or the like.
A source voltage for a commercial power source may change on the user side. Furthermore, an input voltage from the commercial power source is not smaller than a rated voltage of the image forming apparatus. In such a case, when temperature control of a fixing section is performed on the same condition, power may be supplied excessively by the heat source, causing the temperature of the fixing member to rise excessively.
In view of the above, in one approach, a voltage applied to the heat source is detected, and based on the detection result, a duty cycle between a time during which power is applied to the heat source and a time during which power is not applied to the heat source per unit time is controlled in accordance with the detected voltage, to control power consumption.
Although a voltage can be detected at a position close to the commercial power source without application of a voltage to the heat source, power supply to the fixing device or the use of another electric device using the same power source may cause fluctuation in applied voltage to the fixing device. However, it is necessary to turn on the heat source for one to two seconds with a duty cycle of 100% in order to detect a more accurate voltage while power is applied to the fixing device. In a case in which a voltage larger than a rated voltage is applied to the heat source and the heat source is turned on with a duty cycle of 100%, the temperature of the fixing device may rise excessively. In particular, in the case of using a thin roller or belt for the fixing member, the temperature of the fixing member tends to rise easily, causing the temperature of the fixing member to rise beyond the acceptable range.
In view of the above, there is demand for a fixing device capable of accurately detecting an applied voltage to a heat source and also capable of preventing an excessive temperature rise of the fixing member, and an image forming apparatus including the fixing member.